BMW 640i Oxygen Sensor Replacement Cost

Know what price you should pay to get your vehicle fixed.

The average cost for a BMW 640i oxygen sensor replacement is between $562 and $873. Labor costs are estimated between $237 and $300 while parts are priced between $325 and $573. Estimate does not include taxes and fees.

Repairs related to oxygen sensor replacement

What is an oxygen sensor?

The oxygen sensor, or O2 sensor, is a device mounted in the exhaust pipe to constantly monitor the oxygen content in the exhaust gases that exit the engine. The information from the O2 sensor is used by the engine's electronic control unit (ECU) to help determine how much fuel is needed to mix with the air coming into the engine so that the engine may run efficiently. O2 sensors are located ahead of and behind the catalytic converter. A vehicle may have two to five O2 sensors or more.

How does the oxygen sensor work?

The oxygen sensor works to determine if the air/fuel ratio of an engine is rich or lean by sensing the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in the air. It does this by producing voltage when the sensor is heated. The voltage rises and falls as oxygen levels in the exhaust rise and fall. This difference in voltage is fed in real-time to the engine control module which makes adjustments to the air/fuel ratio.

What are the symptoms related to a bad oxygen sensor?

A faulty oxygen sensor is one of the most common causes of a check engine light. Symptoms may include a decrease in fuel mileage, hesitation or misfiring from the engine, rough idling, or even stalling. A faulty sensor may cause the vehicle to fail an emissions test. Oxygen sensors can fail if they are contaminated with oil, coolant, or silicone. If fluid contamination has caused an oxygen sensor failure, the source of the fluid must be resolved or the new sensor may be ruined.

Can I drive with a oxygen sensor problem?

A vehicle that has a bad oxygen sensor can be driven safely until the sensor can be replaced. There are downsides to driving with a faulty sensor. These include increased vehicle emissions and decreased engine performance, such as poor fuel economy, engine hesitation, and rough idle. The check engine light will also remain on until the oxygen sensor has been replaced and the diagnostic trouble code has been cleared.

How often do oxygen sensors need to be replaced?

Oxygen sensors found on older vehicles (through the early nineties) are recommended for replacement between 30k and 50k miles. Heated three- and four-wire sensors found on cars ranging from the mid eighties through the mid nineties should be replaced every 60k miles. Late-model vehicles - those manufactured from 1996 to the present and equipped with OBDII (On Board Diagnostic system) - can go 100k miles or more before the oxygen sensors are scheduled to be replaced.

How are oxygen sensor issues diagnosed?

A faulty oxygen sensor is usually diagnosed by a technician using an OBDII diagnostic scan tool to read the diagnostic code indicated by the check engine light. Depending on variables such as year, make, model, and engine type, there may be two to four sensors on a vehicle – sometimes more. The sensors are arranged in banks (usually on the right and left sides of the engine) and the scan tool alerts a technician as to which sensor is not working properly.

Oxygen Sensor Replacement Cost Estimates

The average cost for an Oxygen Sensor Replacement is between $562 and $873 but can vary from car to car.

How is a oxygen sensor replaced?

A technician will perform a scan of the vehicle's diagnostic system (OBD II) to determine the location of the faulty oxygen sensor. Once the bad sensor has been found, the vehicle (in most cases) must be safely lifted and supported on a hoist (or a jack and jack stands) to provide access to the exhaust system. The bad sensor is disconnected from the wiring harness. Using a special oxygen sensor tool, the technician will remove the sensor from its mount and replace it with a new sensor. It is not uncommon for a technician to have to use heat to get the oxygen sensor to come loose.

OBD codes related to Oxygen Sensor Replacement

RepairPal Recommendations for oxygen sensor issues

RepairPal recommends using only high quality OEM oxygen sensors as opposed to cheaper aftermarket replacements that may not be recognized by a vehicle's computer.

What to look out for when dealing with oxygen sensor issues

Because of the location of the oxygen sensor in the exhaust stream where exhaust components are subject to repeated heating and cooling, the oxygen sensor may be difficult to remove from its mount. A technician often needs to use a torch to heat the sensor mount during removal to keep from breaking the sensor and causing further damage. Also, because of the inherent danger of lifting a vehicle, strict safety procedures should be followed before this repair is attempted.

Can I replace the oxygen sensor myself?

This is a relatively simple intermediate-level DIY repair that does not require many tools. The repair does, however, require the ability to use a scan tool to determine which oxygen sensor needs to be replaced, the ability to safely lift and support the vehicle on a hoist or with a jack and jack stands, and (most likely) the experience to use heat - an oxy-acetylene or propane torch - to aid in removal of the oxygen sensor. There is always a chance that, despite a technician's best efforts, an old sensor might break upon removal. If this happens it is important to have experience to extract the broken sensor from its mount - or the ability to take the vehicle to a repair facility.